/* Thread edges through blocks and update the control flow and SSA graphs.
Copyright (C) 2004-2013 Free Software Foundation, Inc.
This file is part of GCC.
GCC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.
GCC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3. If not see
. */
#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tree.h"
#include "flags.h"
#include "basic-block.h"
#include "function.h"
#include "gimple.h"
#include "gimple-iterator.h"
#include "gimple-ssa.h"
#include "tree-phinodes.h"
#include "tree-ssa.h"
#include "tree-ssa-threadupdate.h"
#include "dumpfile.h"
#include "cfgloop.h"
#include "hash-table.h"
#include "dbgcnt.h"
/* Given a block B, update the CFG and SSA graph to reflect redirecting
one or more in-edges to B to instead reach the destination of an
out-edge from B while preserving any side effects in B.
i.e., given A->B and B->C, change A->B to be A->C yet still preserve the
side effects of executing B.
1. Make a copy of B (including its outgoing edges and statements). Call
the copy B'. Note B' has no incoming edges or PHIs at this time.
2. Remove the control statement at the end of B' and all outgoing edges
except B'->C.
3. Add a new argument to each PHI in C with the same value as the existing
argument associated with edge B->C. Associate the new PHI arguments
with the edge B'->C.
4. For each PHI in B, find or create a PHI in B' with an identical
PHI_RESULT. Add an argument to the PHI in B' which has the same
value as the PHI in B associated with the edge A->B. Associate
the new argument in the PHI in B' with the edge A->B.
5. Change the edge A->B to A->B'.
5a. This automatically deletes any PHI arguments associated with the
edge A->B in B.
5b. This automatically associates each new argument added in step 4
with the edge A->B'.
6. Repeat for other incoming edges into B.
7. Put the duplicated resources in B and all the B' blocks into SSA form.
Note that block duplication can be minimized by first collecting the
set of unique destination blocks that the incoming edges should
be threaded to.
Block duplication can be further minimized by using B instead of
creating B' for one destination if all edges into B are going to be
threaded to a successor of B. We had code to do this at one time, but
I'm not convinced it is correct with the changes to avoid mucking up
the loop structure (which may cancel threading requests, thus a block
which we thought was going to become unreachable may still be reachable).
This code was also going to get ugly with the introduction of the ability
for a single jump thread request to bypass multiple blocks.
We further reduce the number of edges and statements we create by
not copying all the outgoing edges and the control statement in
step #1. We instead create a template block without the outgoing
edges and duplicate the template. */
/* Steps #5 and #6 of the above algorithm are best implemented by walking
all the incoming edges which thread to the same destination edge at
the same time. That avoids lots of table lookups to get information
for the destination edge.
To realize that implementation we create a list of incoming edges
which thread to the same outgoing edge. Thus to implement steps
#5 and #6 we traverse our hash table of outgoing edge information.
For each entry we walk the list of incoming edges which thread to
the current outgoing edge. */
struct el
{
edge e;
struct el *next;
};
/* Main data structure recording information regarding B's duplicate
blocks. */
/* We need to efficiently record the unique thread destinations of this
block and specific information associated with those destinations. We
may have many incoming edges threaded to the same outgoing edge. This
can be naturally implemented with a hash table. */
struct redirection_data : typed_free_remove
{
/* A duplicate of B with the trailing control statement removed and which
targets a single successor of B. */
basic_block dup_block;
/* The jump threading path. */
vec *path;
/* A list of incoming edges which we want to thread to the
same path. */
struct el *incoming_edges;
/* hash_table support. */
typedef redirection_data value_type;
typedef redirection_data compare_type;
static inline hashval_t hash (const value_type *);
static inline int equal (const value_type *, const compare_type *);
};
/* Simple hashing function. For any given incoming edge E, we're going
to be most concerned with the final destination of its jump thread
path. So hash on the block index of the final edge in the path. */
inline hashval_t
redirection_data::hash (const value_type *p)
{
vec *path = p->path;
return path->last ()->e->dest->index;
}
/* Given two hash table entries, return true if they have the same
jump threading path. */
inline int
redirection_data::equal (const value_type *p1, const compare_type *p2)
{
vec *path1 = p1->path;
vec *path2 = p2->path;
if (path1->length () != path2->length ())
return false;
for (unsigned int i = 1; i < path1->length (); i++)
{
if ((*path1)[i]->type != (*path2)[i]->type
|| (*path1)[i]->e != (*path2)[i]->e)
return false;
}
return true;
}
/* Data structure of information to pass to hash table traversal routines. */
struct ssa_local_info_t
{
/* The current block we are working on. */
basic_block bb;
/* A template copy of BB with no outgoing edges or control statement that
we use for creating copies. */
basic_block template_block;
/* TRUE if we thread one or more jumps, FALSE otherwise. */
bool jumps_threaded;
};
/* Passes which use the jump threading code register jump threading
opportunities as they are discovered. We keep the registered
jump threading opportunities in this vector as edge pairs
(original_edge, target_edge). */
static vec *> paths;
/* When we start updating the CFG for threading, data necessary for jump
threading is attached to the AUX field for the incoming edge. Use these
macros to access the underlying structure attached to the AUX field. */
#define THREAD_PATH(E) ((vec *)(E)->aux)
/* Jump threading statistics. */
struct thread_stats_d
{
unsigned long num_threaded_edges;
};
struct thread_stats_d thread_stats;
/* Remove the last statement in block BB if it is a control statement
Also remove all outgoing edges except the edge which reaches DEST_BB.
If DEST_BB is NULL, then remove all outgoing edges. */
static void
remove_ctrl_stmt_and_useless_edges (basic_block bb, basic_block dest_bb)
{
gimple_stmt_iterator gsi;
edge e;
edge_iterator ei;
gsi = gsi_last_bb (bb);
/* If the duplicate ends with a control statement, then remove it.
Note that if we are duplicating the template block rather than the
original basic block, then the duplicate might not have any real
statements in it. */
if (!gsi_end_p (gsi)
&& gsi_stmt (gsi)
&& (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND
|| gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO
|| gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH))
gsi_remove (&gsi, true);
for (ei = ei_start (bb->succs); (e = ei_safe_edge (ei)); )
{
if (e->dest != dest_bb)
remove_edge (e);
else
ei_next (&ei);
}
}
/* Create a duplicate of BB. Record the duplicate block in RD. */
static void
create_block_for_threading (basic_block bb, struct redirection_data *rd)
{
edge_iterator ei;
edge e;
/* We can use the generic block duplication code and simply remove
the stuff we do not need. */
rd->dup_block = duplicate_block (bb, NULL, NULL);
FOR_EACH_EDGE (e, ei, rd->dup_block->succs)
e->aux = NULL;
/* Zero out the profile, since the block is unreachable for now. */
rd->dup_block->frequency = 0;
rd->dup_block->count = 0;
}
/* Main data structure to hold information for duplicates of BB. */
static hash_table redirection_data;
/* Given an outgoing edge E lookup and return its entry in our hash table.
If INSERT is true, then we insert the entry into the hash table if
it is not already present. INCOMING_EDGE is added to the list of incoming
edges associated with E in the hash table. */
static struct redirection_data *
lookup_redirection_data (edge e, enum insert_option insert)
{
struct redirection_data **slot;
struct redirection_data *elt;
vec *path = THREAD_PATH (e);
/* Build a hash table element so we can see if E is already
in the table. */
elt = XNEW (struct redirection_data);
elt->path = path;
elt->dup_block = NULL;
elt->incoming_edges = NULL;
slot = redirection_data.find_slot (elt, insert);
/* This will only happen if INSERT is false and the entry is not
in the hash table. */
if (slot == NULL)
{
free (elt);
return NULL;
}
/* This will only happen if E was not in the hash table and
INSERT is true. */
if (*slot == NULL)
{
*slot = elt;
elt->incoming_edges = XNEW (struct el);
elt->incoming_edges->e = e;
elt->incoming_edges->next = NULL;
return elt;
}
/* E was in the hash table. */
else
{
/* Free ELT as we do not need it anymore, we will extract the
relevant entry from the hash table itself. */
free (elt);
/* Get the entry stored in the hash table. */
elt = *slot;
/* If insertion was requested, then we need to add INCOMING_EDGE
to the list of incoming edges associated with E. */
if (insert)
{
struct el *el = XNEW (struct el);
el->next = elt->incoming_edges;
el->e = e;
elt->incoming_edges = el;
}
return elt;
}
}
/* For each PHI in BB, copy the argument associated with SRC_E to TGT_E. */
static void
copy_phi_args (basic_block bb, edge src_e, edge tgt_e)
{
gimple_stmt_iterator gsi;
int src_indx = src_e->dest_idx;
for (gsi = gsi_start_phis (bb); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple phi = gsi_stmt (gsi);
source_location locus = gimple_phi_arg_location (phi, src_indx);
add_phi_arg (phi, gimple_phi_arg_def (phi, src_indx), tgt_e, locus);
}
}
/* We have recently made a copy of ORIG_BB, including its outgoing
edges. The copy is NEW_BB. Every PHI node in every direct successor of
ORIG_BB has a new argument associated with edge from NEW_BB to the
successor. Initialize the PHI argument so that it is equal to the PHI
argument associated with the edge from ORIG_BB to the successor. */
static void
update_destination_phis (basic_block orig_bb, basic_block new_bb)
{
edge_iterator ei;
edge e;
FOR_EACH_EDGE (e, ei, orig_bb->succs)
{
edge e2 = find_edge (new_bb, e->dest);
copy_phi_args (e->dest, e, e2);
}
}
/* Given a duplicate block and its single destination (both stored
in RD). Create an edge between the duplicate and its single
destination.
Add an additional argument to any PHI nodes at the single
destination. */
static void
create_edge_and_update_destination_phis (struct redirection_data *rd,
basic_block bb)
{
edge e = make_edge (bb, rd->path->last ()->e->dest, EDGE_FALLTHRU);
rescan_loop_exit (e, true, false);
e->probability = REG_BR_PROB_BASE;
e->count = bb->count;
/* We have to copy path -- which means creating a new vector as well
as all the jump_thread_edge entries. */
if (rd->path->last ()->e->aux)
{
vec *path = THREAD_PATH (rd->path->last ()->e);
vec *copy = new vec ();
/* Sadly, the elements of the vector are pointers and need to
be copied as well. */
for (unsigned int i = 0; i < path->length (); i++)
{
jump_thread_edge *x
= new jump_thread_edge ((*path)[i]->e, (*path)[i]->type);
copy->safe_push (x);
}
e->aux = (void *)copy;
}
else
{
e->aux = NULL;
}
/* If there are any PHI nodes at the destination of the outgoing edge
from the duplicate block, then we will need to add a new argument
to them. The argument should have the same value as the argument
associated with the outgoing edge stored in RD. */
copy_phi_args (e->dest, rd->path->last ()->e, e);
}
/* Wire up the outgoing edges from the duplicate block and
update any PHIs as needed. */
void
ssa_fix_duplicate_block_edges (struct redirection_data *rd,
ssa_local_info_t *local_info)
{
edge e = rd->incoming_edges->e;
vec *path = THREAD_PATH (e);
/* If we were threading through an joiner block, then we want
to keep its control statement and redirect an outgoing edge.
Else we want to remove the control statement & edges, then create
a new outgoing edge. In both cases we may need to update PHIs. */
if ((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK)
{
edge victim;
edge e2;
/* This updates the PHIs at the destination of the duplicate
block. */
update_destination_phis (local_info->bb, rd->dup_block);
/* Find the edge from the duplicate block to the block we're
threading through. That's the edge we want to redirect. */
victim = find_edge (rd->dup_block, (*path)[1]->e->dest);
e2 = redirect_edge_and_branch (victim, path->last ()->e->dest);
e2->count = path->last ()->e->count;
/* If we redirected the edge, then we need to copy PHI arguments
at the target. If the edge already existed (e2 != victim case),
then the PHIs in the target already have the correct arguments. */
if (e2 == victim)
copy_phi_args (e2->dest, path->last ()->e, e2);
}
else
{
remove_ctrl_stmt_and_useless_edges (rd->dup_block, NULL);
create_edge_and_update_destination_phis (rd, rd->dup_block);
}
}
/* Hash table traversal callback routine to create duplicate blocks. */
int
ssa_create_duplicates (struct redirection_data **slot,
ssa_local_info_t *local_info)
{
struct redirection_data *rd = *slot;
/* Create a template block if we have not done so already. Otherwise
use the template to create a new block. */
if (local_info->template_block == NULL)
{
create_block_for_threading (local_info->bb, rd);
local_info->template_block = rd->dup_block;
/* We do not create any outgoing edges for the template. We will
take care of that in a later traversal. That way we do not
create edges that are going to just be deleted. */
}
else
{
create_block_for_threading (local_info->template_block, rd);
/* Go ahead and wire up outgoing edges and update PHIs for the duplicate
block. */
ssa_fix_duplicate_block_edges (rd, local_info);
}
/* Keep walking the hash table. */
return 1;
}
/* We did not create any outgoing edges for the template block during
block creation. This hash table traversal callback creates the
outgoing edge for the template block. */
inline int
ssa_fixup_template_block (struct redirection_data **slot,
ssa_local_info_t *local_info)
{
struct redirection_data *rd = *slot;
/* If this is the template block halt the traversal after updating
it appropriately.
If we were threading through an joiner block, then we want
to keep its control statement and redirect an outgoing edge.
Else we want to remove the control statement & edges, then create
a new outgoing edge. In both cases we may need to update PHIs. */
if (rd->dup_block && rd->dup_block == local_info->template_block)
{
ssa_fix_duplicate_block_edges (rd, local_info);
return 0;
}
return 1;
}
/* Hash table traversal callback to redirect each incoming edge
associated with this hash table element to its new destination. */
int
ssa_redirect_edges (struct redirection_data **slot,
ssa_local_info_t *local_info)
{
struct redirection_data *rd = *slot;
struct el *next, *el;
/* Walk over all the incoming edges associated associated with this
hash table entry. */
for (el = rd->incoming_edges; el; el = next)
{
edge e = el->e;
vec *path = THREAD_PATH (e);
/* Go ahead and free this element from the list. Doing this now
avoids the need for another list walk when we destroy the hash
table. */
next = el->next;
free (el);
thread_stats.num_threaded_edges++;
if (rd->dup_block)
{
edge e2;
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
e->src->index, e->dest->index, rd->dup_block->index);
rd->dup_block->count += e->count;
/* Excessive jump threading may make frequencies large enough so
the computation overflows. */
if (rd->dup_block->frequency < BB_FREQ_MAX * 2)
rd->dup_block->frequency += EDGE_FREQUENCY (e);
/* In the case of threading through a joiner block, the outgoing
edges from the duplicate block were updated when they were
redirected during ssa_fix_duplicate_block_edges. */
if ((*path)[1]->type != EDGE_COPY_SRC_JOINER_BLOCK)
EDGE_SUCC (rd->dup_block, 0)->count += e->count;
/* Redirect the incoming edge (possibly to the joiner block) to the
appropriate duplicate block. */
e2 = redirect_edge_and_branch (e, rd->dup_block);
gcc_assert (e == e2);
flush_pending_stmts (e2);
}
/* Go ahead and clear E->aux. It's not needed anymore and failure
to clear it will cause all kinds of unpleasant problems later. */
delete_jump_thread_path (path);
e->aux = NULL;
}
/* Indicate that we actually threaded one or more jumps. */
if (rd->incoming_edges)
local_info->jumps_threaded = true;
return 1;
}
/* Return true if this block has no executable statements other than
a simple ctrl flow instruction. When the number of outgoing edges
is one, this is equivalent to a "forwarder" block. */
static bool
redirection_block_p (basic_block bb)
{
gimple_stmt_iterator gsi;
/* Advance to the first executable statement. */
gsi = gsi_start_bb (bb);
while (!gsi_end_p (gsi)
&& (gimple_code (gsi_stmt (gsi)) == GIMPLE_LABEL
|| is_gimple_debug (gsi_stmt (gsi))
|| gimple_nop_p (gsi_stmt (gsi))))
gsi_next (&gsi);
/* Check if this is an empty block. */
if (gsi_end_p (gsi))
return true;
/* Test that we've reached the terminating control statement. */
return gsi_stmt (gsi)
&& (gimple_code (gsi_stmt (gsi)) == GIMPLE_COND
|| gimple_code (gsi_stmt (gsi)) == GIMPLE_GOTO
|| gimple_code (gsi_stmt (gsi)) == GIMPLE_SWITCH);
}
/* BB is a block which ends with a COND_EXPR or SWITCH_EXPR and when BB
is reached via one or more specific incoming edges, we know which
outgoing edge from BB will be traversed.
We want to redirect those incoming edges to the target of the
appropriate outgoing edge. Doing so avoids a conditional branch
and may expose new optimization opportunities. Note that we have
to update dominator tree and SSA graph after such changes.
The key to keeping the SSA graph update manageable is to duplicate
the side effects occurring in BB so that those side effects still
occur on the paths which bypass BB after redirecting edges.
We accomplish this by creating duplicates of BB and arranging for
the duplicates to unconditionally pass control to one specific
successor of BB. We then revector the incoming edges into BB to
the appropriate duplicate of BB.
If NOLOOP_ONLY is true, we only perform the threading as long as it
does not affect the structure of the loops in a nontrivial way.
If JOINERS is true, then thread through joiner blocks as well. */
static bool
thread_block_1 (basic_block bb, bool noloop_only, bool joiners)
{
/* E is an incoming edge into BB that we may or may not want to
redirect to a duplicate of BB. */
edge e, e2;
edge_iterator ei;
ssa_local_info_t local_info;
struct loop *loop = bb->loop_father;
/* To avoid scanning a linear array for the element we need we instead
use a hash table. For normal code there should be no noticeable
difference. However, if we have a block with a large number of
incoming and outgoing edges such linear searches can get expensive. */
redirection_data.create (EDGE_COUNT (bb->succs));
/* If we thread the latch of the loop to its exit, the loop ceases to
exist. Make sure we do not restrict ourselves in order to preserve
this loop. */
if (loop->header == bb)
{
e = loop_latch_edge (loop);
vec *path = THREAD_PATH (e);
if (path
&& (((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK && joiners)
|| ((*path)[1]->type == EDGE_COPY_SRC_BLOCK && !joiners)))
{
for (unsigned int i = 1; i < path->length (); i++)
{
edge e2 = (*path)[i]->e;
if (loop_exit_edge_p (loop, e2))
{
loop->header = NULL;
loop->latch = NULL;
loops_state_set (LOOPS_NEED_FIXUP);
}
}
}
}
/* Record each unique threaded destination into a hash table for
efficient lookups. */
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (e->aux == NULL)
continue;
vec *path = THREAD_PATH (e);
if (((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK && !joiners)
|| ((*path)[1]->type == EDGE_COPY_SRC_BLOCK && joiners))
continue;
e2 = path->last ()->e;
if (!e2 || noloop_only)
{
/* If NOLOOP_ONLY is true, we only allow threading through the
header of a loop to exit edges.
There are two cases to consider. The first when BB is the
loop header. We will attempt to thread this elsewhere, so
we can just continue here. */
if (bb == bb->loop_father->header
&& (!loop_exit_edge_p (bb->loop_father, e2)
|| (*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK))
continue;
/* The second occurs when there was loop header buried in a jump
threading path. We do not try and thread this elsewhere, so
just cancel the jump threading request by clearing the AUX
field now. */
if ((bb->loop_father != e2->src->loop_father
&& !loop_exit_edge_p (e2->src->loop_father, e2))
|| (e2->src->loop_father != e2->dest->loop_father
&& !loop_exit_edge_p (e2->src->loop_father, e2)))
{
/* Since this case is not handled by our special code
to thread through a loop header, we must explicitly
cancel the threading request here. */
delete_jump_thread_path (path);
e->aux = NULL;
continue;
}
}
if (e->dest == e2->src)
update_bb_profile_for_threading (e->dest, EDGE_FREQUENCY (e),
e->count, (*THREAD_PATH (e))[1]->e);
/* Insert the outgoing edge into the hash table if it is not
already in the hash table. */
lookup_redirection_data (e, INSERT);
}
/* We do not update dominance info. */
free_dominance_info (CDI_DOMINATORS);
/* We know we only thread through the loop header to loop exits.
Let the basic block duplication hook know we are not creating
a multiple entry loop. */
if (noloop_only
&& bb == bb->loop_father->header)
set_loop_copy (bb->loop_father, loop_outer (bb->loop_father));
/* Now create duplicates of BB.
Note that for a block with a high outgoing degree we can waste
a lot of time and memory creating and destroying useless edges.
So we first duplicate BB and remove the control structure at the
tail of the duplicate as well as all outgoing edges from the
duplicate. We then use that duplicate block as a template for
the rest of the duplicates. */
local_info.template_block = NULL;
local_info.bb = bb;
local_info.jumps_threaded = false;
redirection_data.traverse
(&local_info);
/* The template does not have an outgoing edge. Create that outgoing
edge and update PHI nodes as the edge's target as necessary.
We do this after creating all the duplicates to avoid creating
unnecessary edges. */
redirection_data.traverse
(&local_info);
/* The hash table traversals above created the duplicate blocks (and the
statements within the duplicate blocks). This loop creates PHI nodes for
the duplicated blocks and redirects the incoming edges into BB to reach
the duplicates of BB. */
redirection_data.traverse
(&local_info);
/* Done with this block. Clear REDIRECTION_DATA. */
redirection_data.dispose ();
if (noloop_only
&& bb == bb->loop_father->header)
set_loop_copy (bb->loop_father, NULL);
/* Indicate to our caller whether or not any jumps were threaded. */
return local_info.jumps_threaded;
}
/* Wrapper for thread_block_1 so that we can first handle jump
thread paths which do not involve copying joiner blocks, then
handle jump thread paths which have joiner blocks.
By doing things this way we can be as aggressive as possible and
not worry that copying a joiner block will create a jump threading
opportunity. */
static bool
thread_block (basic_block bb, bool noloop_only)
{
bool retval;
retval = thread_block_1 (bb, noloop_only, false);
retval |= thread_block_1 (bb, noloop_only, true);
return retval;
}
/* Threads edge E through E->dest to the edge THREAD_TARGET (E). Returns the
copy of E->dest created during threading, or E->dest if it was not necessary
to copy it (E is its single predecessor). */
static basic_block
thread_single_edge (edge e)
{
basic_block bb = e->dest;
struct redirection_data rd;
vec *path = THREAD_PATH (e);
edge eto = (*path)[1]->e;
for (unsigned int i = 0; i < path->length (); i++)
delete (*path)[i];
delete path;
e->aux = NULL;
thread_stats.num_threaded_edges++;
if (single_pred_p (bb))
{
/* If BB has just a single predecessor, we should only remove the
control statements at its end, and successors except for ETO. */
remove_ctrl_stmt_and_useless_edges (bb, eto->dest);
/* And fixup the flags on the single remaining edge. */
eto->flags &= ~(EDGE_TRUE_VALUE | EDGE_FALSE_VALUE | EDGE_ABNORMAL);
eto->flags |= EDGE_FALLTHRU;
return bb;
}
/* Otherwise, we need to create a copy. */
if (e->dest == eto->src)
update_bb_profile_for_threading (bb, EDGE_FREQUENCY (e), e->count, eto);
vec *npath = new vec ();
jump_thread_edge *x = new jump_thread_edge (e, EDGE_START_JUMP_THREAD);
npath->safe_push (x);
x = new jump_thread_edge (eto, EDGE_COPY_SRC_BLOCK);
npath->safe_push (x);
rd.path = npath;
create_block_for_threading (bb, &rd);
remove_ctrl_stmt_and_useless_edges (rd.dup_block, NULL);
create_edge_and_update_destination_phis (&rd, rd.dup_block);
if (dump_file && (dump_flags & TDF_DETAILS))
fprintf (dump_file, " Threaded jump %d --> %d to %d\n",
e->src->index, e->dest->index, rd.dup_block->index);
rd.dup_block->count = e->count;
rd.dup_block->frequency = EDGE_FREQUENCY (e);
single_succ_edge (rd.dup_block)->count = e->count;
redirect_edge_and_branch (e, rd.dup_block);
flush_pending_stmts (e);
return rd.dup_block;
}
/* Callback for dfs_enumerate_from. Returns true if BB is different
from STOP and DBDS_CE_STOP. */
static basic_block dbds_ce_stop;
static bool
dbds_continue_enumeration_p (const_basic_block bb, const void *stop)
{
return (bb != (const_basic_block) stop
&& bb != dbds_ce_stop);
}
/* Evaluates the dominance relationship of latch of the LOOP and BB, and
returns the state. */
enum bb_dom_status
{
/* BB does not dominate latch of the LOOP. */
DOMST_NONDOMINATING,
/* The LOOP is broken (there is no path from the header to its latch. */
DOMST_LOOP_BROKEN,
/* BB dominates the latch of the LOOP. */
DOMST_DOMINATING
};
static enum bb_dom_status
determine_bb_domination_status (struct loop *loop, basic_block bb)
{
basic_block *bblocks;
unsigned nblocks, i;
bool bb_reachable = false;
edge_iterator ei;
edge e;
/* This function assumes BB is a successor of LOOP->header.
If that is not the case return DOMST_NONDOMINATING which
is always safe. */
{
bool ok = false;
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (e->src == loop->header)
{
ok = true;
break;
}
}
if (!ok)
return DOMST_NONDOMINATING;
}
if (bb == loop->latch)
return DOMST_DOMINATING;
/* Check that BB dominates LOOP->latch, and that it is back-reachable
from it. */
bblocks = XCNEWVEC (basic_block, loop->num_nodes);
dbds_ce_stop = loop->header;
nblocks = dfs_enumerate_from (loop->latch, 1, dbds_continue_enumeration_p,
bblocks, loop->num_nodes, bb);
for (i = 0; i < nblocks; i++)
FOR_EACH_EDGE (e, ei, bblocks[i]->preds)
{
if (e->src == loop->header)
{
free (bblocks);
return DOMST_NONDOMINATING;
}
if (e->src == bb)
bb_reachable = true;
}
free (bblocks);
return (bb_reachable ? DOMST_DOMINATING : DOMST_LOOP_BROKEN);
}
/* Return true if BB is part of the new pre-header that is created
when threading the latch to DATA. */
static bool
def_split_header_continue_p (const_basic_block bb, const void *data)
{
const_basic_block new_header = (const_basic_block) data;
const struct loop *l;
if (bb == new_header
|| loop_depth (bb->loop_father) < loop_depth (new_header->loop_father))
return false;
for (l = bb->loop_father; l; l = loop_outer (l))
if (l == new_header->loop_father)
return true;
return false;
}
/* Thread jumps through the header of LOOP. Returns true if cfg changes.
If MAY_PEEL_LOOP_HEADERS is false, we avoid threading from entry edges
to the inside of the loop. */
static bool
thread_through_loop_header (struct loop *loop, bool may_peel_loop_headers)
{
basic_block header = loop->header;
edge e, tgt_edge, latch = loop_latch_edge (loop);
edge_iterator ei;
basic_block tgt_bb, atgt_bb;
enum bb_dom_status domst;
/* We have already threaded through headers to exits, so all the threading
requests now are to the inside of the loop. We need to avoid creating
irreducible regions (i.e., loops with more than one entry block), and
also loop with several latch edges, or new subloops of the loop (although
there are cases where it might be appropriate, it is difficult to decide,
and doing it wrongly may confuse other optimizers).
We could handle more general cases here. However, the intention is to
preserve some information about the loop, which is impossible if its
structure changes significantly, in a way that is not well understood.
Thus we only handle few important special cases, in which also updating
of the loop-carried information should be feasible:
1) Propagation of latch edge to a block that dominates the latch block
of a loop. This aims to handle the following idiom:
first = 1;
while (1)
{
if (first)
initialize;
first = 0;
body;
}
After threading the latch edge, this becomes
first = 1;
if (first)
initialize;
while (1)
{
first = 0;
body;
}
The original header of the loop is moved out of it, and we may thread
the remaining edges through it without further constraints.
2) All entry edges are propagated to a single basic block that dominates
the latch block of the loop. This aims to handle the following idiom
(normally created for "for" loops):
i = 0;
while (1)
{
if (i >= 100)
break;
body;
i++;
}
This becomes
i = 0;
while (1)
{
body;
i++;
if (i >= 100)
break;
}
*/
/* Threading through the header won't improve the code if the header has just
one successor. */
if (single_succ_p (header))
goto fail;
if (latch->aux)
{
vec *path = THREAD_PATH (latch);
if ((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK)
goto fail;
tgt_edge = (*path)[1]->e;
tgt_bb = tgt_edge->dest;
}
else if (!may_peel_loop_headers
&& !redirection_block_p (loop->header))
goto fail;
else
{
tgt_bb = NULL;
tgt_edge = NULL;
FOR_EACH_EDGE (e, ei, header->preds)
{
if (!e->aux)
{
if (e == latch)
continue;
/* If latch is not threaded, and there is a header
edge that is not threaded, we would create loop
with multiple entries. */
goto fail;
}
vec *path = THREAD_PATH (e);
if ((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK)
goto fail;
tgt_edge = (*path)[1]->e;
atgt_bb = tgt_edge->dest;
if (!tgt_bb)
tgt_bb = atgt_bb;
/* Two targets of threading would make us create loop
with multiple entries. */
else if (tgt_bb != atgt_bb)
goto fail;
}
if (!tgt_bb)
{
/* There are no threading requests. */
return false;
}
/* Redirecting to empty loop latch is useless. */
if (tgt_bb == loop->latch
&& empty_block_p (loop->latch))
goto fail;
}
/* The target block must dominate the loop latch, otherwise we would be
creating a subloop. */
domst = determine_bb_domination_status (loop, tgt_bb);
if (domst == DOMST_NONDOMINATING)
goto fail;
if (domst == DOMST_LOOP_BROKEN)
{
/* If the loop ceased to exist, mark it as such, and thread through its
original header. */
loop->header = NULL;
loop->latch = NULL;
loops_state_set (LOOPS_NEED_FIXUP);
return thread_block (header, false);
}
if (tgt_bb->loop_father->header == tgt_bb)
{
/* If the target of the threading is a header of a subloop, we need
to create a preheader for it, so that the headers of the two loops
do not merge. */
if (EDGE_COUNT (tgt_bb->preds) > 2)
{
tgt_bb = create_preheader (tgt_bb->loop_father, 0);
gcc_assert (tgt_bb != NULL);
}
else
tgt_bb = split_edge (tgt_edge);
}
if (latch->aux)
{
basic_block *bblocks;
unsigned nblocks, i;
/* First handle the case latch edge is redirected. We are copying
the loop header but not creating a multiple entry loop. Make the
cfg manipulation code aware of that fact. */
set_loop_copy (loop, loop);
loop->latch = thread_single_edge (latch);
set_loop_copy (loop, NULL);
gcc_assert (single_succ (loop->latch) == tgt_bb);
loop->header = tgt_bb;
/* Remove the new pre-header blocks from our loop. */
bblocks = XCNEWVEC (basic_block, loop->num_nodes);
nblocks = dfs_enumerate_from (header, 0, def_split_header_continue_p,
bblocks, loop->num_nodes, tgt_bb);
for (i = 0; i < nblocks; i++)
if (bblocks[i]->loop_father == loop)
{
remove_bb_from_loops (bblocks[i]);
add_bb_to_loop (bblocks[i], loop_outer (loop));
}
free (bblocks);
/* If the new header has multiple latches mark it so. */
FOR_EACH_EDGE (e, ei, loop->header->preds)
if (e->src->loop_father == loop
&& e->src != loop->latch)
{
loop->latch = NULL;
loops_state_set (LOOPS_MAY_HAVE_MULTIPLE_LATCHES);
}
/* Cancel remaining threading requests that would make the
loop a multiple entry loop. */
FOR_EACH_EDGE (e, ei, header->preds)
{
edge e2;
if (e->aux == NULL)
continue;
vec *path = THREAD_PATH (e);
e2 = path->last ()->e;
if (e->src->loop_father != e2->dest->loop_father
&& e2->dest != loop->header)
{
delete_jump_thread_path (path);
e->aux = NULL;
}
}
/* Thread the remaining edges through the former header. */
thread_block (header, false);
}
else
{
basic_block new_preheader;
/* Now consider the case entry edges are redirected to the new entry
block. Remember one entry edge, so that we can find the new
preheader (its destination after threading). */
FOR_EACH_EDGE (e, ei, header->preds)
{
if (e->aux)
break;
}
/* The duplicate of the header is the new preheader of the loop. Ensure
that it is placed correctly in the loop hierarchy. */
set_loop_copy (loop, loop_outer (loop));
thread_block (header, false);
set_loop_copy (loop, NULL);
new_preheader = e->dest;
/* Create the new latch block. This is always necessary, as the latch
must have only a single successor, but the original header had at
least two successors. */
loop->latch = NULL;
mfb_kj_edge = single_succ_edge (new_preheader);
loop->header = mfb_kj_edge->dest;
latch = make_forwarder_block (tgt_bb, mfb_keep_just, NULL);
loop->header = latch->dest;
loop->latch = latch->src;
}
return true;
fail:
/* We failed to thread anything. Cancel the requests. */
FOR_EACH_EDGE (e, ei, header->preds)
{
vec *path = THREAD_PATH (e);
if (path)
{
delete_jump_thread_path (path);
e->aux = NULL;
}
}
return false;
}
/* E1 and E2 are edges into the same basic block. Return TRUE if the
PHI arguments associated with those edges are equal or there are no
PHI arguments, otherwise return FALSE. */
static bool
phi_args_equal_on_edges (edge e1, edge e2)
{
gimple_stmt_iterator gsi;
int indx1 = e1->dest_idx;
int indx2 = e2->dest_idx;
for (gsi = gsi_start_phis (e1->dest); !gsi_end_p (gsi); gsi_next (&gsi))
{
gimple phi = gsi_stmt (gsi);
if (!operand_equal_p (gimple_phi_arg_def (phi, indx1),
gimple_phi_arg_def (phi, indx2), 0))
return false;
}
return true;
}
/* Walk through the registered jump threads and convert them into a
form convenient for this pass.
Any block which has incoming edges threaded to outgoing edges
will have its entry in THREADED_BLOCK set.
Any threaded edge will have its new outgoing edge stored in the
original edge's AUX field.
This form avoids the need to walk all the edges in the CFG to
discover blocks which need processing and avoids unnecessary
hash table lookups to map from threaded edge to new target. */
static void
mark_threaded_blocks (bitmap threaded_blocks)
{
unsigned int i;
bitmap_iterator bi;
bitmap tmp = BITMAP_ALLOC (NULL);
basic_block bb;
edge e;
edge_iterator ei;
/* Move the jump threading requests from PATHS to each edge
which starts a jump thread path. */
for (i = 0; i < paths.length (); i++)
{
vec *path = paths[i];
edge e = (*path)[0]->e;
e->aux = (void *)path;
bitmap_set_bit (tmp, e->dest->index);
}
/* If optimizing for size, only thread through block if we don't have
to duplicate it or it's an otherwise empty redirection block. */
if (optimize_function_for_size_p (cfun))
{
EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi)
{
bb = BASIC_BLOCK (i);
if (EDGE_COUNT (bb->preds) > 1
&& !redirection_block_p (bb))
{
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (e->aux)
{
vec *path = THREAD_PATH (e);
delete_jump_thread_path (path);
e->aux = NULL;
}
}
}
else
bitmap_set_bit (threaded_blocks, i);
}
}
else
bitmap_copy (threaded_blocks, tmp);
/* Look for jump threading paths which cross multiple loop headers.
The code to thread through loop headers will change the CFG in ways
that break assumptions made by the loop optimization code.
We don't want to blindly cancel the requests. We can instead do better
by trimming off the end of the jump thread path. */
EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi)
{
basic_block bb = BASIC_BLOCK (i);
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (e->aux)
{
vec *path = THREAD_PATH (e);
/* Basically we're looking for a situation where we can see
3 or more loop structures on a jump threading path. */
struct loop *first_father = (*path)[0]->e->src->loop_father;
struct loop *second_father = NULL;
for (unsigned int i = 0; i < path->length (); i++)
{
/* See if this is a loop father we have not seen before. */
if ((*path)[i]->e->dest->loop_father != first_father
&& (*path)[i]->e->dest->loop_father != second_father)
{
/* We've already seen two loop fathers, so we
need to trim this jump threading path. */
if (second_father != NULL)
{
/* Trim from entry I onwards. */
for (unsigned int j = i; j < path->length (); j++)
delete (*path)[j];
path->truncate (i);
/* Now that we've truncated the path, make sure
what's left is still valid. We need at least
two edges on the path and the last edge can not
be a joiner. This should never happen, but let's
be safe. */
if (path->length () < 2
|| (path->last ()->type
== EDGE_COPY_SRC_JOINER_BLOCK))
{
delete_jump_thread_path (path);
e->aux = NULL;
}
break;
}
else
{
second_father = (*path)[i]->e->dest->loop_father;
}
}
}
}
}
}
/* If we have a joiner block (J) which has two successors S1 and S2 and
we are threading though S1 and the final destination of the thread
is S2, then we must verify that any PHI nodes in S2 have the same
PHI arguments for the edge J->S2 and J->S1->...->S2.
We used to detect this prior to registering the jump thread, but
that prohibits propagation of edge equivalences into non-dominated
PHI nodes as the equivalency test might occur before propagation.
This must also occur after we truncate any jump threading paths
as this scenario may only show up after truncation.
This works for now, but will need improvement as part of the FSA
optimization.
Note since we've moved the thread request data to the edges,
we have to iterate on those rather than the threaded_edges vector. */
EXECUTE_IF_SET_IN_BITMAP (tmp, 0, i, bi)
{
bb = BASIC_BLOCK (i);
FOR_EACH_EDGE (e, ei, bb->preds)
{
if (e->aux)
{
vec *path = THREAD_PATH (e);
bool have_joiner = ((*path)[1]->type == EDGE_COPY_SRC_JOINER_BLOCK);
if (have_joiner)
{
basic_block joiner = e->dest;
edge final_edge = path->last ()->e;
basic_block final_dest = final_edge->dest;
edge e2 = find_edge (joiner, final_dest);
if (e2 && !phi_args_equal_on_edges (e2, final_edge))
{
delete_jump_thread_path (path);
e->aux = NULL;
}
}
}
}
}
BITMAP_FREE (tmp);
}
/* Walk through all blocks and thread incoming edges to the appropriate
outgoing edge for each edge pair recorded in THREADED_EDGES.
It is the caller's responsibility to fix the dominance information
and rewrite duplicated SSA_NAMEs back into SSA form.
If MAY_PEEL_LOOP_HEADERS is false, we avoid threading edges through
loop headers if it does not simplify the loop.
Returns true if one or more edges were threaded, false otherwise. */
bool
thread_through_all_blocks (bool may_peel_loop_headers)
{
bool retval = false;
unsigned int i;
bitmap_iterator bi;
bitmap threaded_blocks;
struct loop *loop;
loop_iterator li;
/* We must know about loops in order to preserve them. */
gcc_assert (current_loops != NULL);
if (!paths.exists ())
return false;
threaded_blocks = BITMAP_ALLOC (NULL);
memset (&thread_stats, 0, sizeof (thread_stats));
mark_threaded_blocks (threaded_blocks);
initialize_original_copy_tables ();
/* First perform the threading requests that do not affect
loop structure. */
EXECUTE_IF_SET_IN_BITMAP (threaded_blocks, 0, i, bi)
{
basic_block bb = BASIC_BLOCK (i);
if (EDGE_COUNT (bb->preds) > 0)
retval |= thread_block (bb, true);
}
/* Then perform the threading through loop headers. We start with the
innermost loop, so that the changes in cfg we perform won't affect
further threading. */
FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST)
{
if (!loop->header
|| !bitmap_bit_p (threaded_blocks, loop->header->index))
continue;
retval |= thread_through_loop_header (loop, may_peel_loop_headers);
}
/* Assume we had a jump thread path which went from the latch to the exit
and a path which goes from outside to inside the same loop.
If the latch to exit was handled first, we will thread it and clear
loop->header.
The second path will be ignored by thread_block because we're going
through a loop header. It will also be ignored by the loop above
because loop->header is NULL.
This results in the second path never being threaded. The failure
mode is a dangling AUX field.
This is inherently a bit of a pain to fix, so we just walk all the
blocks and all the incoming edges to those blocks and clear their
AUX fields. */
basic_block bb;
edge_iterator ei;
edge e;
FOR_EACH_BB (bb)
{
FOR_EACH_EDGE (e, ei, bb->preds)
if (e->aux)
{
vec *path = THREAD_PATH (e);
delete_jump_thread_path (path);
e->aux = NULL;
}
}
statistics_counter_event (cfun, "Jumps threaded",
thread_stats.num_threaded_edges);
free_original_copy_tables ();
BITMAP_FREE (threaded_blocks);
threaded_blocks = NULL;
paths.release ();
if (retval)
loops_state_set (LOOPS_NEED_FIXUP);
return retval;
}
/* Delete the jump threading path PATH. We have to explcitly delete
each entry in the vector, then the container. */
void
delete_jump_thread_path (vec *path)
{
for (unsigned int i = 0; i < path->length (); i++)
delete (*path)[i];
path->release();
}
/* Dump a jump threading path, including annotations about each
edge in the path. */
static void
dump_jump_thread_path (FILE *dump_file, vec path)
{
fprintf (dump_file,
" Registering jump thread: (%d, %d) incoming edge; ",
path[0]->e->src->index, path[0]->e->dest->index);
for (unsigned int i = 1; i < path.length (); i++)
{
/* We can get paths with a NULL edge when the final destination
of a jump thread turns out to be a constant address. We dump
those paths when debugging, so we have to be prepared for that
possibility here. */
if (path[i]->e == NULL)
continue;
if (path[i]->type == EDGE_COPY_SRC_JOINER_BLOCK)
fprintf (dump_file, " (%d, %d) joiner; ",
path[i]->e->src->index, path[i]->e->dest->index);
if (path[i]->type == EDGE_COPY_SRC_BLOCK)
fprintf (dump_file, " (%d, %d) normal;",
path[i]->e->src->index, path[i]->e->dest->index);
if (path[i]->type == EDGE_NO_COPY_SRC_BLOCK)
fprintf (dump_file, " (%d, %d) nocopy;",
path[i]->e->src->index, path[i]->e->dest->index);
}
fputc ('\n', dump_file);
}
/* Register a jump threading opportunity. We queue up all the jump
threading opportunities discovered by a pass and update the CFG
and SSA form all at once.
E is the edge we can thread, E2 is the new target edge, i.e., we
are effectively recording that E->dest can be changed to E2->dest
after fixing the SSA graph. */
void
register_jump_thread (vec *path)
{
if (!dbg_cnt (registered_jump_thread))
{
delete_jump_thread_path (path);
return;
}
/* First make sure there are no NULL outgoing edges on the jump threading
path. That can happen for jumping to a constant address. */
for (unsigned int i = 0; i < path->length (); i++)
if ((*path)[i]->e == NULL)
{
if (dump_file && (dump_flags & TDF_DETAILS))
{
fprintf (dump_file,
"Found NULL edge in jump threading path. Cancelling jump thread:\n");
dump_jump_thread_path (dump_file, *path);
}
delete_jump_thread_path (path);
return;
}
if (dump_file && (dump_flags & TDF_DETAILS))
dump_jump_thread_path (dump_file, *path);
if (!paths.exists ())
paths.create (5);
paths.safe_push (path);
}